Image display panel having antistatic film with transparent and electroconductive properties and process for processing same

ABSTRACT

There are disclosed an image display panel having an antistatic film comprising a SiO 2  coat of transparent and electroconductive properties on the front surface of said panel; the coat containing fine particles of at least one compound selected from electroconductive metal oxides and hygroscopic metal salts; and a process for producing the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image display panels and a process forproducing the same, and more particularly, to image display panels,especially screen panels of cathode ray tubes, the front surfaces ofwhich are improved in antistatic properties and if necessary, coatedwith films best suited for minimizing the reflection of external light,and to a process for producing such panels.

2. Description of Related Art

Transparent base plates made of glass or the like are used for imagedisplay panels, as represented by those of cathode ray tubes and liquidcrystal display devices. It is desired to inhibit these image displaypanels from electrification, i.e. being charged with electricity, andfrom the reflection of external light.

As regards the inhibition of electrification, the wide use ofexplosion-proof cathode ray tubes in recent years has brought about theuselessness of the front protecting glasses of television receivers orof other display devices and, in consequence, the front parts of cathoderay tubes have become bare. This has caused matters such that a personupon directly touching the front part (panel) of a cathode ray tube, isstrongly shocked by high voltage electrostatic charge present on thepanel surface. Moreover, the electrified panel surface absorbsatmospheric dirt or dust, which accumulates and fouls the panel surface.This raises the problem of images formed on the panel being hard to see.Taking a cathode ray tube (a color Braun tube or a display Braun tube)as an example, the cause of the electrification will now be explained.As shown in FIG. 4 of the accompanying drawings, a thin uniform aluminumfilm 4 is vapor-deposited on a phosphor coat 3 laid on the inner wall ofthe glass panel 7 of the cathode ray tube 1. When a power supply to thecathode ray tube is turned on or off, a high positive-pole voltage isapplied to the aluminum film 4 or shut off therefrom. To oppose thishigh voltage on the inside aluminum film, electric charge develops, thatis, electrostatic induction generates electric charge on the outer wallof the panel 7.

In addition, the outer surfaces of the panels (image display panels) ofBraun tubes are glassy and hence are liable to strongly reflect externallight, making it difficult to read images formed on the panels.Recently, in particular, display devices comprising various cathode raytubes, besides television receivers, have been used widely as terminalsof information machines and apparatus. Therefore the problem of thisexternal-light reflection has become taken up extensively in the fieldof VDT (visual display terminal). For such reasons, a very strong needfor anti-reflection films has been growing.

Thus, demand has become very strong for image display panels providedwith the function of inhibiting the reflection of external light,particularly the functions of inhibiting both reflection andelectrification.

For inhibiting electrification of the faces of image display panels,there are the method of forming transparent electroconductive coats onthe front surfaces of Braun tubes in television receivers and variousterminal display devices and grounding these coats; the method (Jap.Pat. Appln. Kokai No. 61-118932) of utilizing airborne moisture, that isthe method of leaving small amounts of hydroxy groups in Si—O—Si chains(or networks) formed from the hydrolysis of alkoxysilane applied on thepanel face, the hydroscopic nature of which lowers the electricresistance of the glass surfaces of the panels to levels of 10⁹ to 10¹⁰Ω; and the method (Japanese Patent Application Kokai (Laid-Open) No.61-118932) of stopping en route the decomposition of a silicon alkoxidesuch as ethyl silicate applied on the panel faces, thereby leaving somesilanol groups (—Si—OH) in the Si—O—Si siloxane structure.

For the formation of transparent electroconductive films, there areknown, for example, the method, as shown in Japanese Utility PatentPublication No. 49-24211, of applying an electroconductor solution byspray coating and burning the coats at 450° C. to form transparentconductive films, the method of forming such films by vacuum depositionor sputtering, and the method, as shown in Japanese Patent ApplicationKokai Nos. 62-154540 and 62-116436, of forming transparent conductivefilms or extra fine conductive wires in the form of strips or nets.

For inhibiting the panel faces from reflecting external light, there areknown, for example, the method of forming so-called telepanels coveredwith multilayer anti-reflecting films (AR coats), by vapor depositionand adhering these telepanels on the panel faces and the method ofspraying the panel faces with an alcoholic solution of Si(OR₁)₄ (R₁ isalkyl), followed by burning to form coats having minute projectionsconsisting of SiO₂ particles.

Further, conventional panels inhibited from the reflection of externallight include, for example, glass panels the surfaces of which areetched with silicofluoric acid (H₂SiF₆) to form projections ordepressions of 50 to 30,000 Å height or depth and 100 to 2,000 Å pitch,thereby imparting a reflection inhibiting function (U.S. Pat. No.2,490,662) and glass panels the surfaces of which are sprayed with analcoholic solution of alkoxysilane Si(OR₁)₄ and then subjected toburning to form SiO₂ coats having fine projections or depressions(Japanese Patent Application Kokai No. 61-118932).

The method of utilizing atmospheric moisture to inhibit theelectrification is effective in locations where humidity is relativelyhigh, but exhibits no antistatic effect in locations where humidity islow. In addition, the film fixing temperature cannot be raised over 80°C. because some silanol groups (—Si—OH) must be left in the filmconstitution (at higher temperatures all the silanol groups convert toform the Si—O—SiO siloxane structure). The coating films formed at suchlow temperatures exhibit very low strengths and are gradually peeled offby rubbing with a cloth.

Vapor deposition methods are not fitted for mass production, since theygenerally require large-scale apparatus for vacuum deposition,sputtering, CVD (chemical vapor deposition), or the like and needtreatment in vacuo. Moreover, these methods involve significant problemsin fabrication cost as well as in increase in throughput. Theabove-mentioned method of forming transparent conductive films in theform of strips requires more operation steps, requiring high productioncosts. The formation of extra fine conductor wires in the form of stripshas many problems in production cost and in product performance.

According to the method of imparting a reflection inhibiting function byetching, the etching leaves a deposit on the treated surface and theetched surface, damaged chemically, has low abrasion strength, that is,rubbing the etched surface readily removes projections therefrom,reducing the reflection inhibiting effect remarkably.

According to the method of spraying an alcoholic solution of Si(OR₁)₄,sprayed liquid particles are deposited more thinly toward the center ofthe object glass panel face, that is, more thickly toward the periphery.Hence it is difficult to form uniform unevenness throughout the glasssurface. This raises the problem of such panels displaying images of lowdegrees of resolution.

According to the method of spraying an alcoholic solution of Si(OR₁)₄directly against the panel faces of cathode ray tubes, followed byburning to form SiO₂ coats have minute projections or depressions,sufficient anti-glare effect can be obtained and the production costsare low, but the burning for the purpose of fortifying the coatsdecreases the content of hydroxy groups and hence increases the surfaceresistivities. Therefore the intended antistatic effect cannot beobtained.

According to the method of adhering telepanels provided with AR coats byvapor deposition, excellent reflection inhibiting efficiency can beachieved, but the antistatic effect cannot be obtained since the ARcoats consist of an insulator, and in addition the fabrication cost ishigh.

SUMMARY OF THE INVENTION

An object of the invention is to provide image display panels superiorin antistatic function.

Another object of the invention is to provide a process for producingimage display panels superior in antistatic function.

A further object of the invention is to provide image display panelssuperior in both antistatic and reflection inhibiting functions.

A still further object of the invention is to provide a process forproducing image display panels superior in both antistatic andreflection inhibiting functions.

The fist aspect of the invention is directed to an image display panel,particularly a cathode ray tube panel, having an antistatic coat formedon the outer surface thereof by applying a suspension of at least one oftin oxide, indium oxide, and antimony oxide in an alcoholic solution ofalkoxysilane [Si(OR₁)₄, wherein R₁ is alkyl] on the front surface of animage display panel and the subjecting the coated panel to heattreatment at relatively low temperatures.

The second aspect of the invention is directed to an image displaypanel, particularly a cathode ray tube panel, the outer surface of whichis coated with a film having both antistatic and reflection inhibitingfunctions.

The third aspect of the invention is directed to a process for producingimage display panels, particularly cathode ray tubes, which comprisesapplying a suspension of at least one of tin oxide, indium oxide, andantimony oxide in an alcoholic solution of alkoxysilane on the frontsurface of an image display panel, particularly the panel of a cathoderay tube, and subjecting the coated panel to heat treatment atrelatively low temperatures to form an antistatic film.

The fourth aspect of the invention is directed to a process forproducing image display panels, particularly cathode ray tubes, theouter surfaces of which are coated with films having both antistatic andreflection inhibiting functions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sketch drawing showing an embodiment of the invention.

FIG. 2 is a schematic partially sectional view of an embodiment of theinvention.

FIGS. 3(a) and 3(b) are a partially sectional view of a cathode ray tubeshowing schematically an embodiment of the invention and an enlargedsectional view showing the underlying electroconductive coat and thereflection inhibiting coat of the cathode ray tube, respectively.

FIG. 4 is a schematic fragmentary sectional view for explaining theelectrification of the panel of cathode ray tube.

FIG. 5 is an illustration for explaining the principle of inhibitinglight reflection.

FIG. 6 is an enlarged sectional view of an outermost surface part of areflection inhibiting coat, the view showing schematically anotherembodiment of the invention.

FIGS. 7(a) and 7(b), similarly to FIGS. 3(a) and 3(b), are a fragmentarysectional view of a cathode ray tube and an enlarged sectional view ofthe reflection inhibiting coat of the cathode ray tube.

FIG. 8 is a graph showing electric charge decay characteristics, i.e.electric charge decay curves, of Braun tubes obtained in Example 1 ofthis specification.

FIG. 9 is a graph to illustrate the antistatic effect of the coatingfilm obtained in Example 2.

FIG. 10 is a graph showing results of measuring reflectivities of areflection inhibiting coat which is an embodiment of the invention incomparison with results of measuring those of a conventional coat.

FIG. 11 is a graph showing antistatic effects of an electroconductivecoat which is an embodiment of the invention in comparison with theantistatic effect of a conventional coat.

In these drawings;

1 . . . Cathode ray tube

2 . . . Antistatic coat (or transparent conductive coat)

2′ . . . Underlying conductive coat

3 . . . phosphor

4 . . . Aluminum film

6 . . . Reflection inhibiting coat

6a . . . Fine SiO₂ particle

6b . . . Thin SiO₂ film

7 . . . Panel

8 . . . Anti-glare coat

9 . . . Auxiliary band

14 . . . Curve for Braun tube of present invention

15 . . . Curve for untreated Braun tube

16 . . . Curve for Braun tube treated with ethoxysilane alone

17 . . . Curve for antistatic coat of present invention

18 . . . Curve for conventional coat

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to an image display panel comprisingan antistatic film formed on the front surface of said panel andconstructed of a transparent electroconductive coating film formed bySiO₂ thin film-like material founded firmly onto said front surface;said film contains particles of at least one compound selected fromelectroconductive metal oxides and hygroscopic metal salts, and aprocess for producing such image display panels.

In this case, the SiO₂ film may be formed of either one layer or twolayers. This coat may have an external-light reflection inhibitingfunction (hereinafter abbreviated as reflection inhibiting function) inaddition to transparent and electroconductive properties. This type ofcoat may be formed of either a single layer comprising a member havingtransparent and electroconductive properties with a member having areflection inhibiting function of a double-layer structure formed of anunderlying layer having transparency and electric conductivity and anoverlying layer having a reflection inhibiting function.

Therefore the image display panel of the invention is roughly classifiedinto two types of panels. One type thereof, corresponding to the firstaspect of the invention, comprises an antistatic layer which consistsessentially of a transparent electroconductive coating film. This typeof panel is fitted chiefly for cathode ray tubes. The other type ofpanel, corresponding to the second aspect of the invention, comprises anantistatic layer or a coating film having both an antistatic functionand a reflection inhibiting (hereinafter often referred to as non-glare)function. This type of panel includes one having an antistatic layercombining an antistatic function and a reflection inhibiting function.Such panels, in particular, are adaptable for liquid crystal displaypanels and the like which are not particularly required to have strongantistatic properties. The third aspect is a process for producing imagedisplay panels of the first aspect and the fourth aspect is a processfor producing panels of the second aspect.

In the first place, image display panels according to the first aspectare described. An essential component of this type panel is anelectroconductive metal oxide. Coating this metal oxide layer with SiO₂film yields the intended image display panel.

The first aspect is described below in more detail.

The display panel of the first aspect of the present invention comprisesan antistatic thin SiO₂ film formed on the front surface of said panel.The film contains fine particles of at least one metal oxide such asSnO₂, In₂O₃, SbO₂O₃ and the like.

The first aspect of the invention can be achieved by suspending fineparticles of tin oxide (SnO₂), indium oxide (In₂O₃), antimony oxide(Sb₂O₃), or a mixture of these metal oxides, the particles themselvesbeing transparent and electroconductive, in an alcoholic solution ofalkoxysilane [Si(OR₁)₄; R₁ is alkyl], applying this suspension by spincoating on the front surfaces of the panels of Braun tubes and the like,and then heat-treating the coatings at temperatures of up to 200° C. toform transparent, electroconductive, antistatic coating films.

The panel display of the first aspect can be easily fabricated since itis possible to exhibit sufficient effects by using fine particles havingper se transparent and electroconductive properties with heat treatmentat a temperature of up to 200° C. without requiring any such hightemperature as about 500° C., which is necessary in the liquid coatingmethod to decompose an organic metal compound.

The above particles, having sizes of up to thousands of Å, arepractically invisible with human eyes and do not scatter light notappreciably, hence forming a very transparent film. The materialconnecting these particles together is Si(OR₁)₄, which on heating at200° C. for 30 minutes adheres to glass with sufficiently strong forceand acts as a binder to consolidate securely the transparent conductiveparticles, thus resulting in a film having improved strength.

The thickness of the transparent conductive film, depending upon itscomponent materials, is up to 2000 Å, preferably from 50 to 500 Å, forpractical use.

The transparent conductive film optionally contains a hygroscopic metalsalt. Such metal salts include salts of inorganic acids such ashydrochloric acid, nitric acid, and sulfuric acid and salts of organicacids such as carboxylic acids. Suitable metals for such metal saltsinclude those of group II represented by magnesium and those of groupIII represented by aluminum.

To the above suspension may be added a dispersing medium selected fromacetylacetone, other ketones, and ethyl Cellosolve; water as adecomposition reactant; and an inorganic acid such as nitric acid as acatalyst for promoting the decomposition, in necessary amounts.

The spin coating can be carried out by using generally about 10-50 ml ofthe suspension of a 20-inch cathode ray tube. In this case, sufficientamounts of SnO₂, In₂O₃, and Sb₂O₃ applied alone or in mixture are about0.5-1.0 mg/cm² of the panel surface area.

The heat treatment can be carried out at about 100° C. for a short time,generally for 5-10 minutes, and then at 150°-200° C., preferably160°-180° C., for about 25-30 minutes. These conditions are sufficient.

In the first aspect, the heat treatment (burning) of the coating can beaccomplished at temperatures of up to 200° C. Accordingly, thesuspension can be applied directly on the panels and therefore cathoderay tubes adequate to satisfy quality requirements can be supplied atvery low prices.

In the second aspect of the invention, an antistatic function can beimparted effectively by using a transparent electroconductive metaloxide such SnO₂, In₂O₃, or Sb₂O₃ or a hygroscopic metal salt. Areflection inhibiting function can be imparted effectively by using fineSiO₂ particles having specific sizes or by forming an antistatic filmand further forming an SiO₂ film from an alkoxysilane compound.

More specifically, the first embodiment of the second aspect is, forexample, an image display panel such as the panel of cathode ray tubewhich comprises an antistatic SiO₂ thin film having a non-glare functionformed on the front surface of said panel and fine projections of thesurface of said film, the projections being formed by the particles ofSiO₂. The film contains fine particles of at least one metal oxideselected from SnO₂, In₂O₃, Sb₂O₃ and the like. The display can beprovided with an antistatic function and a reflection inhibitingfunction by applying an alcoholic suspension containing at least one ofSnO₂, and Sb₂O₃ and alkoxysilane on the front surface of the panel ofcathode ray tube or the like, converting the resulting coat to atransparent conductive film by preliminary burning, applying further analcoholic solution of an alkoxysilane compound by spray coating on thetransparent conductive film, and burning the whole to form an SiO₂ coathaving fine projections.

The second embodiment is, for example, an image display panel such asthe panel of cathode ray tube, the front surface of the panel beingcoated with a transparent conductive film which in turn is covered witha non-glare SiO₂ film containing fine SiO₂ particles of 100-10,000 Å indiameter.

The third embodiment is, for example, an image display panel such as thepanel of cathode ray tube, the L front surface of the panel beingcovered with a SiO₂ thin film (or coat) having non-glare function aswell containing fine SiO₂ particles of 100-10,000 Å in diameter and anadditive selected from hygroscopic metal salt particles and conductivemetal oxide particles.

In the above first and second embodiments, the thickness of thetransparent conductive film, which is used as an underlayer for thenon-glare film (or coat), depends upon the materials composing thetransparent conductive film. For practical use, this thickness isdesirably up to 2000 Å, preferably from 50 to 500 Å.

The transparent conductive film, particularly in the second embodiment,may be a thin SiO₂ film into which such a transparent conductive metaloxide and/or a hygroscopic metal salt as mentioned above has beenincorporated to impart conductivity. The hygroscopic metal saltcontained in the above thin SiO₂ film may be a salt with an inorganicacid such as hydrochloric acid, nitric acid or sulfuric acid or a saltwith an organic acid such as a carboxylic acid. Preferred metal saltsinclude salts of group II metals represented by magnesium and salts ofgroup III metals represented by aluminum. These metal salts absorbmoisture from the atmosphere to lower the electric resistance of thepanel surface. The conductive metal oxide, on the other hand, whichitself has conductivity, is preferred to the metal salt for the purposeof lowering the electric resistance of the panel surface. While theconductivity imparting metal oxide and/or metal salts, even when itscontent is too low, exhibits its effect a little, suitable contentsthereof are 0.01-1.0 mg/cm², particularly 0.15-0.3 mg/cm², of surfacearea of the thin SiO₂ film. The lower limit of the above range isdefined from the minimum requirements as properties of conductivity filmand the upper limit is from the lower limit of adhesive strength of theSiO₂ film to the panel surface.

The underlying conductive film must have such thickness and propertiesas to have practically no adverse effect on the performancecharacteristics of the overlying reflection inhibiting film (or coat).The above stated conductive film according to the invention satisfiesthese requirements.

In the second embodiment the reflection inhibiting film needs to containfine SiO₂ particles of 100-10,000 Å in diameter.

These diameters (average diameters) of fine SiO₂ particles arerestricted from the relation between the degree of image resolution andthe reflection inhibiting effect. The lower limit of diameters isdefined in view of the reflection inhibiting effect, that is to say,when the diameter is less than 100 Å, the intended reflection inhibitingeffect is difficult to obtain. On the other hand, the upper limit isdefined in view of the degree of resolution. When the diameter exceeds10,000 Å, the degree of resolution lowers remarkably. Accordingly, whilethe above range has been defined as a practically acceptable range, thediameter is desirably 500-1200 Å, preferably 500-600 Å, particularlypreferably about 550 Å.

When the amount of fine SiO₂ particles fixed on the panel surface (or onthe conductive film) is small, the effect is observed a little. Forpractical use, the amount is 0.01-1 mg/cm², preferably 0.1-0.3 mg/cm²,of surface area of the substrate. This range has been defined forreasons similar to those in the case of the SiO₂ particle diameter. Thatis, the lower limit has been defined in view of the reflectioninhibiting effect while the upper limit in view of the degree ofresolution.

In the third embodiment, the reflection inhibiting film can formed tocontain the above stated fine SiO₂ particles and an additive composed ofthe above stated metal oxide and/or metal salt. In this case, the metaloxide used can be selected from generally known conductive metal oxidesincluding those having perovskite structures. The incorporation of atleast one of the above stated additives will suffice.

The third aspect of the invention is directed to a process for producingimage display panels, particularly cathode ray tubes, which comprisesmixing fine particles of at least one compound selected from transparentconductive SnO₂, In₂O₃, Sb₂O₃ and the like with an alcoholic solution ofalkoxysilane to form a suspension, applying this suspension on the frontsurface of an image display panel such as a Braun tube panel, andheating the resulting coat at temperatures of up to 200° C. to form atransparent conductive film having an antistatic function.

The alcohol is desired to have the same number of carbon atoms as doesthe alkyl of the alkoxysilane used to form thin SiO₂ films.

The alkoxysilane is represented by the general formula Si(OR₁)₄ whereinR₁ is alkyl. Generally, preferred alkyls have 1 to 5 carbon atoms.

For coating panel surfaces or other substrates, spin coating and dipcoating methods can be used.

Materials and conditions used in the third aspect will be describedlater together with those used in the fourth aspect since many of thematerials and conditions are common to both aspects.

Similarly to the second aspect, the fourth aspect includes threeembodiments, which are described separately in brief.

The first embodiment is a process for producing image display panelssuch as cathode ray tube, which comprises coating the front surface ofan image display panel with an alcoholic solution containing analkoxysilane and at least one of SnO₂, In₂O₃, and Sb₂O₃, burning theresulting coat preliminarily to convert it into a transparent conductivefilm, then spray-coating this film with an alcoholic solution ofalkoxysilane, and burning the whole to form a conductive coat havingfine SiO₂ projections at its surface.

The second embodiment is a process for producing image display panelssuch as cathode ray tubes, which comprises the steps of: forming atransparent conductive film on the front surface of an image displaypanel; dispersing fine SiO₂ particles of 100-10,000 Å in diameter in analcoholic solution of alkoxysilane Si(OR₁)₄, wherein R₁ is alkyl, andapplying this dispersion on the transparent conductive film formed onthe front surface of the panel; and heating the resulting coat todecompose the Si(OR₁)₄ contained therein and form a thin SiO₂ film,thereby coating and fixing the fine SiO₂ particles with the thin SiO₂film.

In the first place, the step of forming the transparent conductive filmis described in detail. Since this film is formed on an image displaypanel such as the panel of a cathode ray tube, it is desirable to formthis film under such conditions, particularly temperature conditions (upto about 500° C.), as to give no strain to the glass plate whichconstructs the panel. The film may be formed according to any methodthat satisfies the above noted requirement. A typical method to form thetransparent conductive film is illustrated below.

When the film is formed of at least one conductive metal oxide selectedfrom SnO₂, In₂O₃, and Sb₂O₃, there are known, for example, the followingmethods (1) and (2) to form the film directly on the glass panel. (1) Atarget formed of at least one of the above metal oxides is fixed in asputtering apparatus with the target itself being opposed to the glasspanel, and a metal oxide film is formed by sputtering on the panelsurface. (2) Using an organic metal compound as a raw material, aconductive metal oxide film is formed on the glass panel by thegenerally known CVD process. In this method (2), suitable organic metalcompounds for use include alkyl metal compounds represented by M(R₁)_(m) and alkoxy metal compounds represented by M (OR₁)_(m), whereinM denotes Sn, In or Sb, m denotes the valency of M, and R₁ denotes alkyl(C_(n)H_(2n+1), n=1 to 5 for practical use). Specific examples of theorganic metal compound include Sn(CH₃)₄ and Sn(OC₂H₅)₄. However, thismethod is not preferable for the practical use due to high temperatureburning.

Therefore, it would be better to form the thin SiO₂ film by hydrolyzingan alkoxy silane Si(OR₁)₄, wherein R₁ is alkyl and n=1 to 5 forpractical use. In the present invention, at least one additive, asdescribed in detail in the explanation of the second aspect of theinvention, selected from transparent conductive metal oxides andhygroscopic metal salts is added to an alcoholic solution of saidSi(OR₁)₄ for the purpose of imparting conductivity to the objectivefilm, this mixture in liquid form is applied on the panel surface, andthe coating surface is heated to decompose the Si(OR₁)₄, thereby forminga thin SiO₂ film. The additive is used in an amount desirably from 0.05to 7%, preferably from 1.0 to 2.0% by weight based on the alcoholicsolution.

Of the above-mentioned additives, the transparent conductive metal oxideis insoluble but dispersed in the alcoholic solution while the metalsalt is dissolved partly or entirely. For the purpose of forming a thinSiO₂ having good conductivity, it is desirable to disperse or dissolvethe additive thoroughly in the alcoholic solution. In view of the above,a ketone (e.g. acetylacetone) or ethyl cellosolve is preferably added asa dispersing medium to the alcoholic solution. Moreover, water and aninorganic acid catalyst, e.g. nitric acid, are preferably added tofacilitate the hydrolysis of Si(OR₁)₄.

The alcohol to solve the Si(OR₁)₄ is desired to have the same alkylgroup as the R₁ or Si(OR₁)₄. A most useful alcoholic solution ofSi(OR₁)₄ is composed of tetraethoxysilane Si(OC₂H₅)₄ (R₁ is ethyl) as asolute and ethyl alcohol as a solvent.

The above stated alcoholic solution is applied on the panel surface by acoating method such as spin coating, dip coating, spray coating or acombination of these methods.

The heat treatment of the coating surface to decompose the Si(OR₁)₄ andthereby form a thin SiO₂ film is carried out at temperatures desirablyfrom 50° to 200° C., preferably from 160° to 180° C. Because the heattreatment is carried out at relatively low temperatures, this method offorming a thin conductive SiO₂ film is advantageous over theconventional film forming methods (1) and (2) mentioned above. When thismethod is applied to cathode ray tubes, e.g. Braun tubes, completedbulbs can be treated. Hence, this method is best suited for massproduction processes. Needless to say, this method is also applicable toBraun tubes and the like before completion of the bulbs, that is, in thecourse of the production of the tubes.

In the second place, detailed description is given on the step offorming the non-glare film on the substrative transparent conductivefilm.

The alcoholic solution of alkoxysilane (alkyl silicate) Si(OR₁)₄ isprepared in the following manner. Both Si(OR₁)₄, which is the source ofthe thin SiO₂ film, and the solvent alcohol are the same as in the caseof the thin SiO₂ film formation, which has been described above(formation of underlying transparent conductive film). Therefore,detailed description of Si(OR₁)₄ and the alcohol is omitted.

Fine SiO₂ particles of 100-10,000 Å in diameter are dispersed in analcoholic solution of Si(OR₁)₄ prepared as described above. The amountof said particles is desirably from 0.1 to 10%, preferably from 1 to 3%,by weight based on the alcoholic solution from the viewpoint of thereflection inhibiting effect and the degree of image resolution. Aketone (e.g. acetylacetone) or ethyl Cellosolve, acting as a dispersingmedium, is preferably added to the alcoholic solution for the purpose ofsecuring a sufficient dispersion and moreover, water and inorganic acidcatalyst, e.g. nitric acid are preferably added to facilitate thehydrolysis of Si(OR₁)₄.

Moreover, while the use of Si(OR₁)₄ Where R₁ is ethyl in the formationof reflection inhibiting films has been illustrated, alkoxysilanesSi(OR₁)₄ having 1 to 5 carbon atoms in R₁ are favorable, as satedbefore, in other words, where R₁ is represented by C_(n)H_(2n+1), n isdesired to be from 1 to 5; when n=1, 3, 4, or 5, effects achieved aresimilar to those achieved when n=2. However, since the viscosity of thealcoholic solution increases slightly with an increase in n, it isrecommendable to choose an alcohol fitted as a solvent for thealkoxysilane to use in consideration of the workability. A most usefulalcoholic solution of Si(OR₁)₄ is composed of tetraethoxysilane(R₁=ethyl) as solute and ethyl alcohol as a solvent.

The above stated dispersion of fine SiO₂ particles in an alcoholicsolution of Si(OR₁)₄ is applied on the transparent conductive substratefilm by a coating method such as spin coating, dip coating, spraycoating, or a combination of these methods, as mentioned above(formation of thin conductive film of SiO₂).

When the Si(OR₁)₄ is decomposed by heating the coating surface to form athin SiO₂ film (or coat) and cover and fix the dispersed fine SiO₂particles with the film, the heating temperature is desirably from 50°to 200° C., preferably from 160° to 180° C.

The reflection inhibiting film is formed as described above, wherein theheat treatment temperature, similarly to the case of the underlying filmstated above, is relatively low. Hence, this method of formingreflection inhibiting films is favorable for the formation such films onthe panel surfaces of completed cathode ray tubes.

The underlying transparent conductive film thus formed, adherentintimately to the panel surface, exhibits the effect of reducing theelectric resistance of the panel surface. The film composed of a metaloxide having per se conductivity or the thin SiO₂ film in which aconductive metal oxide is dispersed shows the reduction of surfaceresistivity caused by the same principle as in the case of a so-calledtransparent conductive film. The antistatic function is maintained bythis reduction. In case of the thin SiO₂ film containing a hygroscopicmetal salt, on the other hand, conductivity is imparted due to theabsorption and retention of moisture by the metal salt. The metal saltretains its hygroscopicity after being subjected to the heat treatmentto hydrolyze the Si(OR₁)₄ (this heat treatment improves the filmstrength), not losing its function but having the action of reducing theresistivity of panel surface. Of the additives to be contained in thethin SiO₂ film, the conductive metal oxide is superior to thehygroscopic metal salt in the function of reducing the resistivity ofpanel surface. In particular, oxides of tin, indium, and antimony arefavorable in that the resulting films are superior in transparency andcan maintain high degrees of image resolution. Unlike metal oxides,certain metal salts are fixed in melted form in the film. In such acase, the film is superior in transparency and retains a high degree ofimage resolution.

The reflection inhibiting film, in which fine SiO₂ particles aredispersed uniformly and fixed with a thin SiO₂ film, has fine uniformprojections at the outermost surface, said projections being constructedof fine SiO₂ particles covered with the thin SiO₂ film. This surfacehaving fine uniform projections scatters external light, thus exhibitingreflecting inhibiting effect.

The third embodiment is a process for producing image display panels,which comprises the steps of; dispersing fine SiO₂ particles of100-10,000 Å in diameter and particles of at least one additive selectedfrom hygroscopic metal salts and conductive metal oxides in an alcoholicsolution of alkoxysilane Si(OR₁)₄; applying this dispersion on the frontsurface of an image display panel and heating the coating surface todecompose the Si(OR₁)₄, thereby forming a thin SiO₂ film to cover andfix the fine SiO₂ particles with the thin SiO₂ film, thus forming a filmhaving non-glare function as well on the front surface of the panel.

The amounts of materials and the manner of using materials, in thisembodiment, are almost the same as in the second embodiment. Thereforethe description of the amounts and of the manner are omitted. In thisembodiment, however, there is no step of forming such a transparentconductive film as is formed in the second embodiment. After applicationof the alkyl silicate solution, the heat treatment is conducted to formthe thin SiO₂ film.

When the Si(OR₁)₄ is decomposed by heating the coating surface to form athin SiO₂ film, the heating temperature is desirably from 50° to 200°C., preferably from 160° to 180° C. Since the heat treatment in thisembodiment is carried out at such relatively low temperatures, completedbulbs can be treated when this method is applied to cathode ray tubes,e.g. Braun tubes. Hence, this method is best suited for mass productionprocesses. Needless to say, this method is also applicable to Brauntubes and the like before completion of the bulbs, that is, in thecourse of the production of the tubes.

In the thus formed film having non-glare function as well fine SiO₂particles uniformly dispersed, as stated above, are covered and fixed onthe glass plate (substrate) with a thin film of SiO₂ formed by thehydrolysis of Si(OR₁)₄. These uniformly dispersed fine SiO₂ particlespermit the retention of reflection inhibiting effect and of the highdegree of image resolution. Moreover the thin SiO₂ film contains theadditive, i.e., a conductive metal oxide and/or a hygroscopic metalsalt, which retains its hygroscopicity after being subjected to the heattreatment to hydrolyze the Si(OR₁)₄ (this heat treatment improves thefilm strength), not losing its function but having the action ofreducing the resistivity of panel surface. On the other hand, when theconductive metal oxide is used, the reduction of surface resistivity isobserved which is caused by the same principle as in the case of aso-called transparent conductive film. The antistatic function ismaintained by those reductions of surface resistivity. Of the additivesused in the invention, which exhibits antistatic effect, the conductivemetal oxide is superior to the hygroscopic metal salt in the function ofreducing the surface resistivity of substrate. In particular, oxides ofmetals such as tin, indium, and antimony are favorable in that theresulting films are superior in transparency and can maintain highdegrees of image resolution. Unlike metal oxides, certain metal saltsare fixed in melted form in the film. In such a case, the film issuperior in transparency and retains a high degree of image resolution.

The following examples illustrate the present invention, the scope ofwhich is not restricted, of course, by these examples.

EXAMPLE 1

Referring to FIG. 1, this example 1 is explained. An antistatic film 2is formed on the panel surface of a Braun tube 1. A grounded reinforcingband 9 is in contact with the antistatic film 2, maintaining the entiresurface of this film at zero potential.

The antistatic film 2 is formed in the following manner: Fine particlesof any of metal oxides having transparent and conductive propertiesthemselves, e.g. SnO₂, In₂O₃, Sb₂O₃, and mixtures of them, i.e. SnO₂alone, In₂O₃ alone, SnO₂+In₂O₃, SnO₂+In₂O₃+Sb₂O₃, SnO₂+In₂O₃+Sb₂O₃ aredispersed thoroughly in an alcoholic solution of ethyl silicateSi(OC₂H₅)₄ to prepare a suspension. To this suspension may be added asuitable dispersing aid (e.g. acetylacetone) and a decompositionpromoting catalyst (e.g. an inorganic acid) in small amounts. For a20-inch Braun tube, about 10 ml of the suspension is consumed.

Then, this suspension is dropped on the panel of Braun tube 1 rotated at100 rpm with the panel surface being directed upward. At the time theapplied suspension spreads all over the surface, the revolution isincreased to 500 rpm, forming a thin uniform coating. This spin coatingis completed in a total time of 1 minute.

Thereafter the coating is dried by heating at 105° C. for about 10minutes, and burned at 160° C. for 30 minutes, thereby forming theantistatic film 2.

FIG. 8 shows electric charge decay characteristic curves for 20-inchcolor display tubes surface-treated in this example. In this drawing;14: the panel coated with the above stated antistatic film according tothe present invention; 15: the panel untreated; 16: the panel having anantistatic coat formed by applying an alcoholic solution of ethylsilicate alone on the untreated panel surface, followed by burning thecoat at 160° C. for 30 minutes to leave some silanol groups. As isevident from FIG. 8, the color display tube provided with the antistaticcoat according to the present invention shows a surface potential decayto 9 kV in about 10 seconds, while the other tubes after 5 minutesretain surface potentials of 20 kV and more, being much inferior inelectric charger decay characteristic.

In the next place, the durability of antistatic coats (formed in themanner described above according to present invention) was examined bymeasuring changes in their surface resistivity. Results were as follows:The change in resistivity when each specimen was rubbed 250 timesreciprocally with an eraser (No. 50—50 of Lion Jimuki Co., Ltd.) under aload of 1 Kg was not more than one figure. The change in surfaceresistivity when each specimen was rubbed 1000 times reciprocally withGURASUKURU (tradename) of Johnson Co. was not more than 0.5 figure. Thechange in surface resistivity when each specimen was immersed in anaqueous NaOH solution of pH 12 at room temperature for 24 hours was alsonot more than one figure. Further, no change was observed in surfaceresistivity when each specimen was placed in an oven of 120° C. for 96hours.

Thus, these panels, having nothing the matter with their antistaticfunction, exhibit this function fully under any environmentalconditions.

In this example, In₂O₃ was found to have the characteristic of providinglower resistivity than does SnO₂.

According to the present invention, the burning of coats can be carriedout below 200° C. and hence completed (but surface-untreated) bulbs canbe directly coated and highly durable antistatic films can be formedwith ease at low costs. In addition, since, high-voltage electric chargegenerated on the thus treated panel surfaces of Braun tubes can beremoved in a moment, the surfaces are prevented from fouling due toatmospheric dust or dirt and thereby the normal distinction of imagescan be retained and moreover electric discharge to human bodies closethe display panels and similar troubles can be avoided.

EXAMPLE 2

Referring to FIG. 2, another embodiment of the present invention isillustrated in detail.

First, the front surface of the panel 7 of a cathode ray tube 1 iscleaned by using an abrasive such as CeO₂ and an alkali detergent suchas (trademark, SILIRON HS supplied by Henkel-Hakusui Corp.). Then thissurface is coated uniformly with an alcoholic solution containing atleast one of SnO₂, In₂O₃, and Sb₂O₃ and Si(OR₁)₄, wherein R₁ is alkyl,by using, for example, a spinner. The above solution was dropped in anamount of about 10 ml for a 14-type cathode ray tube, the revolution ofthe spinner was 600 rpm, and the coating period was 1 minute. However,the coating method is not limited to spin coating but may be dip coatingor spray coating. The coated cathode ray tube was burned preliminarilyat 100°-110° C. for 5 minutes to form a transparent conductive coat 2,which is a substrate film. This substrate cooling to about 50° C. wasspray coated at an air pressure of 3.5 kg/cm² with an alcoholic solutionof Si(OR₁)₄ so as to give a definite gloss. Then the tube was subjectedto main burning at 150°-200° C. for 30 minutes, thereby forming ananti-glare film 8 having fine projections of SiO₂ and high strength.

As to reflective properties of the thus formed anti-glare film 3, the 5°regular (specular) reflectance was 1.5%, which is sufficiently low ascompared with 4.5% said reflectance of the untreated glass panel. Thatis, the anti-glare film 8 was found to have a good reflection inhibitingfunction. Rubbing the surfacer of this film 50 times with an eraser(Lion 50—50) changed the 5° regular reflectance by 0.1% only, provingthe sufficient strength of the film and posing no problem relating tothe anti-glare function.

The antistatic function of the treated surface is illustrated below.FIG. 9, curve 17 shows the relation between time (second) and surfacepotential after switch-off of the 20-type TV receiver according to thisexample (test conditions: temperature 21°-23° C., relative humidity20-23%). Curve 18 in FIG. 9 shows the electric charge decaycharacteristic (such relation as stated above) of a conventional tube,the panel surface thereof being untreated. As can be seen from curve 18,little change was observed in surface potential for the conventionaltube even after 300 seconds. In contrast, the surface potential for thetube according to the present invention, as shown by curve 17, drops toalmost 0 kV in 5 seconds.

As illustrated above, it is possible according to the present inventionto produce cathode ray tubes which have on the front surface of eachpanel a film superior in antistatic function and reflection inhibitingfunction (anti-glare effect) as well as in mechanical strength and areeasy to manufacture in large quantity at low costs.

EXAMPLES 3-6

Transparent conductive substrate films were formed on the front surfacesof the panels (glass panels) of Braun tubes, as shown in Table 1,Examples 3-6.

In Example 3, the conductive film, constructed of SnO₂, was formed byCVD under the following conditions:

Apparatus used: Normal-pressure CVD apparatus

Raw material organo-tin compound: Sn(CH₃)₄

Dopant: Freon gas

Carrier gas: N₂

Substrate temperature (glass panel): 350° C.

In Example 4, the film, constructed of a thin SiO₂ film containing finetransparent conductive SnO₂ particles, was formed in the followingmanner:

(1) Composition of alcoholic solution of alkoxysilane Si(OR₁)₄:

Ethanol (C₂H₅OH): 88 ml

Ethoxysilane (Si(OC₂H₅)₄): 6 ml

Fine transparent conductive powder of SnO₂: 1.2 g

Water: 6 ml

(2) Application of solution on glass panel:

Spinner at 500 rpm

(3) Burning of coat: 160° C., 30 minutes

While In₂O₃, Sb₂O₃, and their mixture were also used as fine transparentconductive powders in place of SnO₂, the results were nearly equal.Therefore SiO₂, as mentioned above, has been taken as a typical example.

In Example 5, the film was formed by depositing an In₂O₃—SnO₂ mixture ona glass panel, as mentioned above, by high-frequency sputtering using anIn₂O₃—SnO₂ (5 wt %) compound target.

In Example 6, the film, constructed of a thin SiO₂ film containingaluminum nitrate Al(NO₃)₃.9H₂O as a hygroscopic metal salt, was formedin the following manner:

(1) Composition of alcoholic solution of alkoxysilane Si(OR₁)₄:

Ethanol (C₂H₅OH): 88 ml

Ethoxysilane (Si(OC₂H₄)₄): 6 ml

Metal salt, Al(NO₃)₃.9H₂O: 1.2 g

Water: 6 ml

(2) Application of solution on glass panel:

Spinner at 500 rpm

(3) Burning of coat film: 160° C., 30 minutes

While AlCl₃, Ca(NO₃)₂, Mg(NO₃)₂, ZnCl₂ and their mixtures were used ashygroscopic metal salts in place of aluminum nitrate, the results werenearly equal. Therefore aluminum nitrate, as mentioned above, has beentaken as a typical example.

Subsequently, conductive substrate films formed as stated above werecoated with reflection inhibiting films in the following manner:

Ethoxysilane [Si(OC₂H₅)₄] is dissolved in ethanol, and water forhydrolysis and nitric acid as a catalyst are added to prepare asolution. To this alcoholic solution are further added 1 wt % of fineSiO₂ particles (nearly sphere-shaped) screened to 500-1000 Å in diameterand a suitable amount of acetylacetone as a dispersing medium todisperse the SiO₂ particles sufficiently.

The thus prepared solution, the composition of which is shown in Table1, is dropped on each conductive substrate film and spread uniformly byusing a spinner.

Thereafter each coat is burnt in the air at 150° C. for about 30 minutesto decompose the ethoxy-silane. Fine SiO₂ particles in the coat arefixed firmly by a thin, uniform, continuous SiO₂ film resulting from thedecomposition, forming fine projections at the surface. Electronmicroscopic observation revealed that the thus formed reflectioninhibiting film has uniform projections or depressions of 1000 Å±200 Åheight or depth and 500 Å pitch at the outermost surface as shown inFIG. 3(b), which is an enlarged view of a cross section shown in FIG.3(a). In FIG. 3(b), 6 denotes the reflection inhibiting film, 6a denotesfine SiO₂ particles, 6b denotes a thin SiO₂ film formed by thedecomposition of ethoxysilane, and 2 denotes the conductive substratefilm.

TABLE 1 Example No. Comparative Item 3 4 5 6 Example Conduc- Main SnO₂SnO₂ In₂O₃ + Hygroscopic Not formed tive sub- component SnO₂ componentstrate in thin film SiO₂ film Forming CVD of Fine SnO₂ SputteringHydrolysis method organo-tin powder + of alkozy- compound Hydrolysissilane of alkoxy- silane Film 100 300 100 100 thickness (Å) Surface 10⁸10⁸ 10⁷ 10¹⁰ resistivity (Ω/square) Composi- Solution of 50 50 50 50 50tion of Si(OC₂H₅)₄ suspen- in ethanol sion for Dispersion 50 50 50 50 50R.I.F.* medium (wt %) (acetylacetone) Property Fine SiO₂ 1 1 1 1 1particles Reflectance 0.4> 0.3> 0.4> 0.3> 0.3> % (5* regular reflection,550 nm) Strength +0.1> +0.1> +0.1> +0.2> +0.1> (increase of reflectanceby 50 times rubbing with eraser) % Time for 10> 10> 15> 25> 200>potential decay to 1 kV after switch off (sec.) Mark *R.I.F. meansreflection inhibiting film

A beam of light of wavelength 550 nm was incident at an incident angleof 5° on the reflection inhibiting film formed as described above onsaid glass panel, and the reflectance was measured. The foundreflectance was less than 0.4%. The reflectances measured similarly butwith the wavelength varied were less than 1% in the wavelength range of450 to 650 nm as shown by curve I of FIG. 10. These values are adequateto satisfy reflectance requirements for VDTs (visual display terminals).

Subsequently, the surface of the reflection inhibiting film formedtogether with the underlying antistatic film on said glass panel, asstated above, was rubbed strongly and uniformly 50 times with an eraser(Lion 50—50). Resulting reflectances, as shown by curve II of FIG. 10,showed shifts of only about 0.1-0.2%, which pose no quality problem.

Curve III of FIG. 10 shows, for comparison, plots of reflectance of asimilar glass panel but subjected to no reflection inhibiting treatment.

The reason for reducing the reflectance of the glass panel by formingsuch a reflection inhibiting film as stated above over the panel surfaceis explained below.

Referring to FIG. 5, which shows a cross section of the reflectioninhibiting film, the reflective index at positions A is that (n_(o)) ofair and n_(o) is about 1. On the other hand, the refractive index atpositions B, where fine SiO₂ particles are present in a packed state, isnearly equal to the refractive index n_(g)=1.48 of glass (SiO₂). Therefractive index in the unevenness part between planes A and B variescontinuously according to the volume fraction of SiO₂. That is, whenextremely thin plates formed by slicing said unevenness part in parallelto planes A and B are supposed, the refractive index (mean value) of anarbitrary one of these supposed plates depends on the proportion of thevolume occupied by the SiO₂ part to the whole volume of this plate.Therefore the refractive index in said unevenness part varies with saidvolume proportion of SiO₂. When the refractive index (mean value) of theextremely thin plate C positioned inside and nearest the plane A isdenoted by n₁ and the refractive index (mean value) of the extremelythin plate D positioned outside and nearest the plane B is denoted byn₂, the condition that the reflectance R at the surface of glass panelon which the above stated reflection inhibiting film is formed becomesthe minimum is:$R = {\frac{( {{n_{1}n_{g}} - {n_{2}n_{o}}} )^{2}}{( {{n_{1}n_{g}} + {n_{2}n_{o}}} )^{2}} = 0}$

Hence, when the condition $n_{g} = \frac{n_{2}}{n_{1}}$

is satisfied, a non-reflecting function (the ability to prevent thereflection of external light completely) is given.

In this case, the value n₂/n₁ depends on the shapes and sizes ofprojections or depressions. Therefore, projections or depressions havingsuch a shape and size as to satisfy the equation n_(g)=n₂/n₁approximately can be formed by coating a suspension of fine SiO₂particles in an alcoholic solution of Si(OR₁)₄, followed by burning thecoat, as described above. Thus it is conceivable that the reflectance aslow as 1% or less has been achieved by forming such ideal projections ordepressions.

The reason for the retention of high mechanical strength by thereflection inhibiting film according to the present invention isconceivably that Si(OR₁)₄ contained in the coat before burning ishydrolyzed as shown by the equation

Si(OC₂H₅)₄+4H₂O→Si(OH)₄+4C₂H₅OH→SiO₂+2H₂O

to form an SiO₂ film, which acts as a strong protective coat.

In addition, screened fine SiO₂ particles effect the formation of fineuniform projections and thus the entire surface has a good reflectioninhibiting function. Further, the fine uniform size of SiO₂ particlesresults in no surface that is more uneven than needs and lowers thedegree of resolution.

In the next place, the antistatic function shown in the bottom line ofTable 1 is explained. FIG. 11 shows the relation between time andsurface potential after switch of a TV receiver. The curve number inFIG. 11 corresponds to the example number in Table 1. In the case ofComparative Example, the surface potential, after 200 seconds, stilldoes not decay to 1 kV or below, that is, the coating film has noantistatic function. Such panel surfaces adsorb dust or dirt from theatmosphere, do not release it, and hence become foul. Images which thesefouled panels display will be hard to see.

The process for the formation of reflection inhibiting films accordingto the present invention can be performed merely by adding fine SiO₂particles, commercially available, to an alcoholic solution of existingSi(OR₁)₄, and applying the resulting suspension on conductive substratefilms formed on completed bulbs, followed by burning the resultingcoats, without using any of harmful chemicals such as hydrofluoric acid.Thus the process can be operated with safety and at low costs.

The shape of fine SiO₂ particles to use is not limited to spheric butmay be irregular as shown in FIG. 6, wherein 6a denotes fine SiO₂particles and 6b denotes a thin SiO₂ film. The average particle size isdesired to be about 100-10,000 Å. When the particle size is less thanabout 100 Å, the outer surface of the resulting film will be too smoothto exhibit sufficient reflection inhibiting effect. On the contrary,when the particle size exceeds about 10,000 Å, the light-diffusingeffect of the resulting surface becomes too large and the degree ofresolution as well as the film strength lower.

The method to apply the suspension of fine SiO₂ particles in alcoholicSi(OR₁)₄ solution is not limited to spin coating, mentioned in the aboveexamples, but may be any of dip coating, spray coating, and combinationof these methods. Suitable temperatures for burning the coat are about50°-200° C.

While Sn(CH₃)₄ was used as a raw material in the formation of theconductive substrate film for CVD purposes in above Example 3, it ispossible, of course, to use other alkyltin compounds Sn(R₁)₄ oralkoxytin compounds SnOR₁)₄ or alternatively, organic compounds ofindium or antimony similar to organic compound of tin. Also the metalsalt to add is not limited to salts of aluminum, calcium, magnesium, andzinc; any metal salt may be used provided that it is hygroscopic. Theaddition of a transparent conductive powder of tin oxide, indium oxide,or antimony oxide, as in Example 2, is favorable in particular since athin SiO₂ film having good conductivity can be formed at relatively lowtemperatures (50°-200° C.) in this case.

As describe above, it is possible according to the present invention toproduce cathode ray tubes provided with coats having an antistaticfunction due to conductive substrate coats and a reflection inhibitingfunction due to reflection inhibiting coats and are mechanically strong.In addition, this process uses no harmful chemical such as hydrofluoricacid and employs relatively low treatment temperatures and simple andsafety unit processes. Thus this process for producing such cathode raytubes is fitted for mass production and the produced panels are superiorin four resistance.

EXAMPLES 7-10

These examples illustrate embodiments where the present invention isapplied to the front surfaces of the panels (glass panels) of Brauntubes.

Ethoxysilane [Si(OC₂H₅)₄] is dissolved in ethanol and water forhydrolysis and nitric acid as a catalyst are added to prepare asolution. To this alcoholic solution are added 1 wt % of fine SiO₂particles (nearly spheric) screened to 500-1000 Å in diameter and asuitable amount of acetylacetone as a dispersing medium.

To the above alcoholic solution, each of different compounds shown inTable 2 were added in a predetermined amount prior to the addition offine SiO₂ particles. Table 2 shows a comparative example wherein nomaterial for antistatic purposes was added, besides Examples 7-10.

Each of compounded suspensions shown in Table 2 is dropped on the glasspanel, and spread uniformly by a spinner.

Thereafter the resulting coat is burnt at 150° C. for about 30 minutesto decompose the ethoxy-silane. The fine SiO₂ particles in the coat arefixed firmly with a thin uniform continuous film of SiO₂ resulting fromthe decomposition, thus forming fine projections or depressions over theglass panel. Electron microscopic observation of a cross section of thethus formed reflection inhibiting film revealed that uniform projectionsor depressions of 1,000 Å±200 Å in height or depth and 500 Å pitch wereformed at the outer surface of the reflection inhibiting film, as shownin FIG. 7(b), which is an enlarged view of the part shown in FIG. 7(a).In FIG. 7(b), 6 denotes the reflection inhibiting film, 6a denotes fineSiO₂ particles, and 6b denotes the thin SiO₂ film resulting from thedecomposition of tetraethoxysilane and containing an antistaticadditive.

TABLE 2 Example No. Comparative Item 7 8 9 10 Example Compo- Addi-Solution of Si(Oc₂H₅)₄ in 50 50 50 50 50 nent tive ethanol (wt %)Al(NO₃)₃·9H₂O (Nitrate 0.5 0.5 — — — of AlCl₃ (chloride) — 0.2 — — —suspen- AlO(CH₃COO)₄·4H₂ O — — 0.7 — — sion (carboxylate) SnO₂(conductive metal — — — 1.0 — oxide) Dispersing medium, Acetylacetone 5050 50 50 50 Fine SiO₂ particle 1.0 1.0 1.0 1.0 1.0 Pro- Reflectance (%),5* regular 0.5> 0.5> 0.5> 0.5> 0.5> perty reflection, 550 nm Surfaceresistivity (Ω/square) 1 × 10⁹> 1 × 10⁸> 1 × 10⁹> 1 × 10⁷> 1 × 10¹²Strength (increase in +0.1> +0.2> +0.1> +0.2> +0.2> reflectance whensurface is rubbed 50 time with eraser)

Reflectance was measured by casting a beam of light of wavelength 550 nmat an incident angle on this reflection inhibiting film formed on saidglass panel. The found reflectance was below 0.5% as shown in Table 2.Further, the reflectances measured similarly but with the wavelengthvaried were less than 1% in the wavelength range of 450 to 650 nm asshown by curve I of FIG. 10. These values are adequate to satisfyreflectance requirements for VDTs.

Subsequently, the surface of the reflection inhibiting film formed onsaid glass panel was rubbed strongly and uniformly 50 times with anerase (Lion 5050). Resulting reflectances, as shown by strength in Table2 and curve II of FIG. 10, showed shifts of only about 0.1-0.2%, whichpose no quality problem. For comparison, the same test was made on asimilar glass panel surface roughened by a conventional etching process.In this case, the reflectance was 2% increased by one rubbing with theeraser. The rubbing 5 times gave the same reflectance as that of thesurface of untreated glass panel, reflectances of which are as shown bycurve III of FIG. 10.

The reason for reducing the reflectance of the glass panel by formingsuch a reflection inhibiting film as stated above can be considered tobe the same as explained in Examples 3-6.

The low surface resistivity, as shown in Table 2, has been achievedconceivably because antistatic components from the suspension acteffectively and do not largely affect the reflection inhibiting functionand the film strength.

Such reflection inhibiting film can be formed directly on completedbulbs merely by adding fine SiO₂ particles, commercially available, toan alcoholic solution of existing Si(OR₁)₄, applying the resultingsuspension, followed by burning the resulting coats, without using anyharmful chemical such as hydrofluoric acid. Thus this film formingprocess can be operated with safety and at low costs.

While the use of Si(OR₁)₄ where R₁ is ethyl has been illustrated in theabove examples, alkoxysilanes Si(OR₁)₄ having 1 to 5 carbon atoms in R₁are useful as stated before. However, since the viscosity of thealcoholic solution increases slightly with an increase in n, it isrecommendable to choose an alcohol fitted as a solvent for thealkoxysilane to use in consideration of the workability.

Moreover, while salts of aluminum have been illustrated as typical metalsalts which are additives to produce antistatic effect, otherhygroscopic salts of groups II and III metals of the periodic tableachieve equivalent antistatic effect. As to conductive metal oxidesalso, SnO₂ has been illustrated as a representative in the aboveexample, other generally known metal oxides, e.g. In₂O₃, Sb₂O₃, complexmetal oxides have perovskite type structures such as LaNiO₃,La_(1-x)Sr_(x)CoO₃ (resistivities of these compounds are all 10⁻⁴ Ωcm atnormal temperature) may be used. In these examples, the shape of fineSiO₂ particles, suspension coating method, and coat burning temperatureand period are the same as in Examples 3-6.

According to the present invention, it is possible to produce imagedisplay panels overlaid with reflection inhibiting films which aresuperior in reflection inhibiting effect and in mechanical strength andalso have an antistatic function. Moreover, these display panels can beproduced by a simple safety process without using any harmful chemicalsuch as hydrofluoric acid, hence being best suited for mass productionand also superior in antifouling property.

What is claimed is:
 1. An image display panel having an antistatic filmcoat comprising a SiO₂ coat of transparent and electroconductiveproperties on the front surface of said panel; said coat containing fineparticles exhibiting or capable of absorbing moisture to impartelectroconductivity, all of said fine particles exhibiting or capable ofabsorbing moisture to impart electroconductivity consisting essentiallyof at least one compound selected from electroconductive metal oxidesand hygroscopic metal salts capable of absorbing moisture to impartelectroconductivity to said coat.
 2. The image display panel of claim 1,wherein the antistatic coat itself either has the non-glare function oris overlaid with a non-glare coat.
 3. The image display panel of claim2, wherein the non-glare coat overlaid on said antistatic coat comprisesa thin SiO₂ film which contains fine SiO₂ particles of 100-10,000 Å indiameter; said particles being coated by said film so as to fix on thesurface of said panel.
 4. The image display panel of claim 3, whereinthe thickness of said antistatic coat is up to 2000 Å and the amount offine SiO₂ particles contained in the non-glare coat is in a range of0.01-1 mg/cm².
 5. The image display panel of claim 4, wherein thethickness of the antistatic coat is 50-500 Å and the amount of said fineSiO₂ particles is in a range of 0.1-0.3 mg/cm².
 6. The image displaypanel of claim 1, wherein said at least one compound is one selectedfrom the group consisting of tin oxide, indium oxide, antimony oxide,chlorides, nitrates, sulfates, and carboxylates of metals of groups IIand III of the periodic table.
 7. The image display panel of claim 1,wherein the content of said at least one compound in said SiO₂ film isin a range of 0.01-1.0 mg/cm² area of the film.
 8. The image displaypanel of claim 1, wherein the antistatic coat is formed as a thin SiO₂film having also reflection inhibitory function and containing furtherfine SiO₂ particles of 100-10,000 Å in diameter in addition to said atleast one compound.
 9. The image display panel of claim 8, wherein saidat least one compound is one selected from the group consisting of saltsof metals of the groups II and III of the periodic table, tin oxide,indium oxide and antimony oxide.
 10. The image display panel of claim 8,wherein said SiO₂ film contains 0.01 to 1.0 mg/cm² of said fine SiO₂particles and 0.01 to 1.0 mg/cm² of said compound, respectively.
 11. Theimage display panel of claim 10, wherein the amount of said fine SiO₂particles contained is 0.1-0.3 mg/cm² and the amount of said at leastone compound of fine particles contained is 0.15-0.3 mg/cm².
 12. Theimage display panel of claim 2, wherein the antistatic coat has itself anon-glare function, and said antistatic coat has fine projections on itssurface and contains fine particles of at least one metal oxide selectedfrom SnO₂, In₂O₃ and Sb₂O₃.
 13. The image display panel of claim 1,wherein said antistatic coat contains fine particles of at least oneelectroconductive metal oxide selected from SnO₂, In₂O₃, and Sb₂O₃ andsaid SiO₂ coat is formed by applying an alcoholic solution ofalkoxysilane [Si(OR₁)₄, wherein R₁ is alkyl] on the front surface ofpanel, followed by heat treatment of the resulting coat at temperaturesof up to 200° C.
 14. The image display panel of claim 1, wherein said atleast one compound is selected from the group consisting of tin oxide,indium oxide and antimony oxide.
 15. The image display panel of claim 1,wherein said at least one compound is selected from the group consistingof chlorides, nitrates, sulfates and carboxylates of metals of groups IIand III of the Periodic Table.
 16. A process for producing image displaypanels which comprises applying a suspension of fine particles of atleast one of electroconductive metal oxides and hygroscopic metal saltsin an alcoholic solution of alkoxysilane on the front surface of panel,followed by heat treatment of the resulting coat to form an antistaticfilm comprising a transparent electroconductive SiO₂ coat on the frontsurface.
 17. The process of claim 16 which comprises forming further anon-glare film on the antistatic film.
 18. The process of claim 17,wherein the formation of a non-glare film comprises the steps of;dispersing fine SiO₂ particles of 100-10,000 Å in diameter in analcoholic solution of alkoxysilane Si(OR₁)₄, wherein R₁ is alkyl,applying the suspension on the antistatic film which is the transparentsubstrate formed on the panel; and heating the resulting coat todecompose the Si(OR₁)₄, forming a thin SiO₂ film, therewith covering andfixing the fine SiO₂ particles.
 19. The process of claim 18 wherein thehygroscopic metal salts are chlorides, nitrates, sulfates, andcarboxylates of metals of groups II and III of the period table and thetransparent conductive metal oxides are of tin, indium, and antimony.20. The process of claim 16, wherein said suspension is prepared bydissolving or dispersing 0.05-7% by weight of the metal oxide or metalsalt in the alcoholic solution of alkoxysilane.
 21. The process of claim16, wherein the first step comprises applying the suspension prepared byfurther adding a ketone or ethyl Cellosolve as a dispersing medium forthe metal salt and metal oxide to the alcoholic solution and also addingwater and, as a catalyst, an inorganic acid for facilitating thehydrolysis of Si(OR₁)₄.
 22. The process of claim 18, wherein saidsuspension is prepared by dispersing 0.1-10% by weight of the fine SiO₂particles in the alcoholic solution of Si(OR₁)₄.
 23. The process ofclaim 18 or 22, wherein R₁ of the alcoholic solution is ethyl alcohol.24. The process of claim 22, wherein said suspension is prepared byfurther adding a ketone or ethyl Cellosolve as a dispersing medium forthe fine SiO₂ particles and also adding water and an inorganic acid forfacilitating the hydrolysis of Si(OR₁)₄.
 25. The process of claim 16,which said suspension is applied by spin coating, dip coating, spraycoating, or combination of these coating methods and the heat treatmentof coating surface is conducted at 50°-200° C.
 26. The process of claim16, wherein said antistatic film is formed by the steps which comprisesdispersing fine SiO₂ particles of 100-10,000 Å in diameter in analcoholic solution of Si(OR₁)₄ wherein R₁ is alkyl; and also dispersingparticles of at least one compound selected from hygroscopic metal saltsand electroconductive metal oxides, applying the resulting suspension onthe antistatic film, heating the resulting coat to decompose theSi(OR₁)₄ and forming a thin SiO₂ film to coat fine SiO₂ particles inorder to fix them on the surface of said panel, whereby said antistaticfilm also has a non-glare function.
 27. The process of claim 27, whereinsaid at least one compound is one selected from the group consisting ofchlorides, nitrates, sulfates, carboxylates of metals of groups II andIII of the periodic table and the oxides of tin, indium, and antimony.28. The process of claim 27 the said fine SiO₂ particles in thealcoholic solution of Si(OR₁)₄ is contained from 0.1 to 10% by weightand said at least one compound in that solution is from 0.05 to 7% byweight.
 29. The process of claim 28, wherein said fine SiO₂ particles iscontained in a range of from 1 to 3% by weight and said at least onecompound from 1.0 to 2.0% by weight.
 30. The process of claim 26,wherein R₁ of the Si(OR₁)₄ is ethyl and the alcohol component of thealcoholic solution consists mainly of ethyl alcohol.
 31. The process ofclaim 30, wherein said suspension is prepared by further adding a ketoneas a dispersing medium for the fine SiO₂ particles to the alcoholicsolution, water and an inorganic acid, as a catalyst, for facilitatingthe hydrolysis of Si(OR₁)₄.
 32. The process of claim 26, wherein saidsuspension is applied by spin coating, dip coating, spray coating, orcombination of these coating methods and the heat treatment of coatingsurface if conducted at 50°-200° C.
 33. The process of claim 17, whereinsaid antistatic film is formed on the front surface of an image displaypanel by applying an alcoholic Si(OR₁)₄ solution, wherein R₁ is alkyl,containing at least one of SnO₂, In₂O₃, and Sb₂O₃ on the front surface,and burning the coat preliminarily, and further said nonglare film isformed on the preliminarily burnt coat by applying an alcoholic solutionof Si(OR₁)₄ by spray coating, and burning the whole coat fully, therebyforming film projections of SiO₂ at the outermost surface.
 34. Theprocess of claim 16, wherein the suspension is a dispersion of fineparticles of at least one of SnO₂, In₂O₃, and Sb₂O₃ in an alcoholicsolution of alkoxysilane Si(OR₁)₄, wherein R₁ is alkyl, and the heattreatment is carried out at temperatures of up to 200° C.
 35. Theprocess of claim 6, wherein said suspension includes anelectroconductive metal oxide selected from the group consisting of tinoxide, indium oxide and antimony oxide.
 36. The process of claim 16,wherein said suspension includes a hygroscopic metal salt selected fromthe group consisting of chlorides, nitrates, sulfates and carboxylatesof metals of groups II and III of the Periodic Table.
 37. The imagedisplay panel of claim 1, wherein said fine particles exhibiting orcapable of absorbing moisture to impart electroconductivity consistessentially of electroconductive metal oxides.
 38. The image displaypanel of claim 37, wherein the antistatic coat itself either has thenon-glare function or is overlaid with a non-glare coat.
 39. The imagedisplay panel of claim 37, wherein the antistatic coat is overlaid witha non-glare coat.
 40. The image display panel of any of claims 37 to 39,wherein the content of said at least one compound in said SiO₂ film isin the range of 0.1-1.0 mg/cm ² area of the film.
 41. The image displaypanel of any of claims 37 to 39, wherein the content of said at leastone compound in said SiO₂ film is in the range of 0.15-0.3 mg/cm ² areaof the film.
 42. The image display panel of any of claims 37 to 39,wherein said antistatic coat has itself a non-glare function, and saidantistatic coat has fine projections on its surface and contains fineparticles of at least one metal oxide selected from SnO ₂ , In ₂ O ₃ andSb ₂ O ₃ .
 43. The image display panel of any one of claims 37 and 39,wherein said fine particles consist essentially of at least one metaloxide selected from SnO₂ , In ₂ O ₃ and Sb ₂ O ₃ .
 44. The image displaypanel of claim 37, wherein said antistatic coat contains fine particlesof at least one electroconductive metal oxide selected from SnO₂ , In ₂O ₃ and Sb ₂ O ₃ and said SiO ₂ coat is formed by applying an alcoholicsolution of alkoxysilane (Si(OR ₁))₄ , wherein R ₁ is alkyl on the frontsurface of panel, followed by heat treatment of the resulting coat attemperatures of up to 200° C.
 45. The image display panel of claim 39,wherein said fine particles consist essentially of at least one metaloxide selected from SnO₂ , In ₂ O ₃ and Sb ₂ O ₃ ; and wherein saidantistatic coat has a thickness up to 2000 Å.
 46. The image displaypanel of claim 45, wherein said antistatic coat has a thickness of50-500 Å.
 47. The image display panel of claim 37, wherein saidantistatic coat is overlaid with a SiO₂ film.
 48. The image displaypanel of claim 47, wherein said SiO₂ film has fine projections.
 49. Theimage display panel of claim 47, wherein said fine particles consistessentially of at least one metal oxide selected from SnO₂ , In ₂ O ₃and Sb ₂ O ₃ ; and wherein said antistatic coat has a thickness up to2000 Å.
 50. The image display panel of claim 47, wherein said antistaticcoat has a thickness of 50-500 Å.
 51. The image display panel of claim48, wherein said fine particles consist essentially of at least onemetal oxide selected from SnO₂ , In ₂ O ₃ and Sb ₂ O ₃ ; and whereinsaid antistatic coat has a thickness up to 2000 Å.
 52. The image displaypanel of claim 48, wherein said antistatic coat has a thickness of50-500 Å.
 53. An image display panel having an antistatic filmcomprising a SiO₂ coat of transparent and electroconductive propertieson the front surface of said panel; said coat containing fine particlesof at least one compound selected from electroconductive metal oxidesand hygroscopic metal salts capable of absorbing moisture to impartelectroconductivity to said coat, wherein said antistatic cost isproduced by applying a suspension of fine particles of at least one ofelectroconductive metal oxides and hygroscopic metal salts in analcoholic solution of alkoxysilane on the front surface of panel,followed by heat treatment of the resulting coat to form an antistaticfilm comprising a transparent electroconductive SiO ₂ coat on the frontsurface.
 54. The image display panel of claim 53, wherein the heattreatment of the resulting coat is conducted at 50°-200° C.
 55. Theimage display panel of claim 53, wherein the heat treatment of theresulting coat is conducted at 160°-180° C.
 56. The image display panelof claim 53, wherein the heat treatment of the resulting coat isconducted without reaching a temperature of 500° C.
 57. An image displaypanel having an antistatic film comprising a SiO₂ coat of transparentand electroconductive properties on the front surface of said panel;said coat containing fine particles of at least one compound selectedfrom electroconductive metal oxides and hygroscopic metal salts capableof absorbing moisture to impart electroconductivity to said coat,wherein said antistatic cost is produced by applying a suspension offine particles of at least one of electroconductive metal oxides andhygroscopic metal salts in a solution of alkoxysilane on the frontsurface of panel, followed by heat treatment of the resulting coatwithout reaching a temperature of 500° C. to form an antistatic filmcomprising a transparent electroconductive SiO ₂ coat on the frontsurface.
 58. The image display panel of claim 57, wherein the heattreatment of the resulting coat is conducted at 50°-200° C.
 59. Theimage display panel of claim 57, wherein the heat treatment of theresulting coat is conducted at 160°-180° C.
 60. The image display panelof any of claims 1-15, wherein said image display is a cathode ray tube.61. The image display panel of any of claims 37 to 39, wherein saidimage display is a cathode ray tube.
 62. The image display panel ofclaim 40, wherein said image display is a cathode ray tube.
 63. Theimage display panel of claim 41, wherein said image display is a cathoderay tube.
 64. The image display panel of claim 42, wherein said imagedisplay is a cathode ray tube.
 65. The image display panel of claim 43,wherein said image display is a cathode ray tube.
 66. The image displaypanel of any of claims 44 to 59, wherein said image display is a cathoderay tube.